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Understanding Wind Power Technology ebook

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Wind energy technology has progressed enormously over the lastdecade. In coming years it will continue to develop in terms ofpower ratings, performance and installed capacity of large windturbines worldwide, with exciting developments in offshoreinstallations. Designed to meet the training needs of wind engineers, thisintroductory text puts wind energy in context, from the naturalresource to the assessment of cost effectiveness and bridges thegap between theory and practice. The thorough coverage spans thescientific basics, practical implementations and the modern stateof technology used in onshore and offshore wind farms forelectricity generation. Key features: * provides in-depth treatment of all systems associated with windenergy, including the aerodynamic and structural aspects of bladedesign, the flow of energy and loads through the wind turbine, theelectrical components and power electronics including controlsystems * explains the importance of wind resource assessment techniques,site evaluation and ecology with a focus of project planning andoperation * describes the integration of wind farms into the electric gridand includes a whole chapter dedicated to offshore windfarms * includes questions in each chapter for readers to test theirknowledge Written by experts with deep experience in research, teachingand industry, this text conveys the importance of wind energy inthe international energy-policy debate, and offers clear insightinto the subject for postgraduates and final year undergraduatestudents studying all aspects of wind engineering. UnderstandingWind Power Systems is also an authoritative resource forengineers designing and developing wind energy systems, energypolicy makers, environmentalists, and economists in the renewableenergy sector.

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Understanding Wind Power Technology

Theory, Deployment and Optimisation

Edited by

Alois Schaffarczyk

University of Applied Sciences, Kiel, Germany

Translated by

Gunther Roth

Adliswil, Switzerland

First published under the title Einführung in die Windenergietechnik by Carl Hanser Verlag © 2012 Carl Hanser Verlag, Munich/FRG. All rights reserved. Authorized translation from the original German language edition published by Carl Hanser Verlag, Munich/FRG

This edition first published 2014© 2014 John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Schaffarczyk, Alois. Understanding wind power technology : theory, deployment and optimisation / by Alois Schaffarczyk.  p. cm. Includes bibliographical references and index.

 ISBN 978-1-118-64751-6 (cloth)1. Wind power. 2. Wind energy conversion systems–Design and construction. I. Title. TJ820.S33 2013 621.31′2136–dc23

2013022982

A catalogue record for this book is available from the British Library.

Preface

Although nearly 20,000 windmills dotted Germany’s landscape by the end of the eighteenth century, the era of modern wind energy began in 1983 when the aptly-named GROWIAN prototype (a German abbreviation for Grosswindanlage, or ‘large wind turbine’) started operation in the German state of Schleswig-Holstein. By the end of 2011, almost 23,000 modern wind turbines had been erected in Germany and supplied nearly 10% of the country’s electricity demand. It took only 30 years for the modern wind industry to develop to the extent that turbines the size and power of the once-colossal GROWIAN had become standard and mass-produced.

At the request of the Carl Hanser Verlag publishing company and under the umbrella of CEwind eG – the consortium for wind energy research between Schleswig-Holstein’s universities – authors from the wind community in Schleswig-Holstein and the Netherlands have collaborated to compile this introductory text on wind energy. Over 11 chapters the interested reader will become familiar with the modern state of this technology.

This text begins with a brief history and then supplements this with an explanation of the importance of wind energy in the international energy policy debate. Following chapters then introduce the aerodynamic and structural aspects of blade design. Then the focus shifts to the flow of energy and loads through the wind turbine, through the powertrain and also the tower-foundation system, respectively. Next, the electrical components such as the generator and power electronics are discussed, including control systems and automation. Following is an explanation of how wind turbines are integrated into the electricity grid, despite the highly fluctuating nature of both this energy source and the grid load; this particular topic is especially relevant for Germany’s transition to renewable energy. The final topic covers one of the youngest and most promising aspects of wind energy: offshore technology.

Kiel, February 2012

For CEwind eG: A.P. Schaffarczyk

English translation: Gunther Roth

About the Authors

Dr H.C. Jos Beurskens previously led the Department for Renewable Energy and Wind Energy at the Dutch research institute for energy (ECN) for over 15 years. He was awarded the Poul-la-Cour Prize for lifetime achievement at the European Wind Energy Association (EWEA) 2008 conference. He is now an independent consultant for technology development and research strategies.

Prof. Dipl.-Ing. Lothar Dannenberg has over 10 years experience with rotor blades and offshore foundations. He has taught classes at the Kiel University of Applied Sciences in these areas, as well as the topics of ship construction and design, fibre composites, and underwater vehicles.

Frank Ehlers has been involved with the development of the German grid connection codes since the passing of the German Renewable Energy Act (in German: Erneuerbare-Energien-Gesetz, EEG), for which he was a member of the federal approval committee. Today he is responsible for the planning and expansion of grid and distribution networks at energy supply company EON Hanse.

Prof. Dr.-Ing. Torsten Faber has served since November 2010 as the Director of the Wind Energy Technology Institute (WETI) at the Flensburg University of Applied Sciences in Germany. He has 10 years of experience in the certification of wind turbines.

Prof. Dr.-Ing. Friedrich W. Fuchs leads the faculty of Power Electronics and Electronic Drives at the Christian-Albrechts-University in Kiel, Germany. One of his group’s main research goals is supporting the transition to renewable energy. He also has 14 years of industrial experience, most recently as Research Director for CONVERTEAM (later renamed General Electrical Power Conversion). He is a founding member and board member of CEwind eG.

Dr Hermann van Radecke has specialised in liaison managing technology transfer between the wind industry and his employer, the Flensburg University of Applied Sciences, for over 20 years. He is also a founding member of CEwind and a lecturer for courses in physics and wind energy. Additionally, he was active in the shaping of the CEwind MSc Wind Engineering programme, previously serving as the program director for Flensburg.

Dr Klaus Rave leads the department of Energy Economics in Schleswig-Holstein and served as an officer in the region’s investment bank for many years. He has been active in many organisations in the international wind community.

Prof. Dr A.P. Schaffarczyk has been involved with wind turbine aerodynamics since 1997. He is a founding member and previous manager of CEwind eG and teaches courses in the CEwind MSc Wind Engineering programme.

Prof. Dr Reiner Johannes Schütt has previously served as the Head of Development and Technical Director of the turbine manufacturer ENERCON NORD Electronic GmbH in Aurich, Germany. Today he teaches and researches in the field of controllers, electrical drives, and wind energy technology at the West Coast University of Applied Sciences in Heide, Germany.

Dipl.-Ing. Sönke Siegfriedsen founded the Aerodyn company in 1983 and still serves as its general manager. His company has developed more than 25 complete wind turbine designs, from which approximately 27,000 examples have been produced (amounting to 31,000 MW of capacity) to date.

Dr Sven Wanser leads the Grid Operation business unit at electricity provider Schleswig-Holstein-Netz AG and teaches the subject of electrical energy technology at the West Coast University of Applied Sciences in Heide, Germany.

1The History of Wind Energy

Jos Beurskens

1.1 Introduction

Wind has been used as a source of energy for more than 1500 years. In times when other sources of energy were unknown or scarce, wind energy represented a successful means for industrial and economic development. Wind energy became a marginal source once cheaper, easier to exploit and easily obtainable sources of energy became available. From the point of view of the contribution of wind energy to economic development, one can divide the history of wind energy into four overlapping time periods (see Figure 1.1). Except in the first period, the emphasis here is the generation of power by wind:

600–1890: Classical period

. Classic windmills for mechanical drives; more than 100,000 windmills in northwestern Europe. The period ended after the discovery of the steam engine and because of the ready availability of wood and coal.

1890–1930: Development of electricity-generating wind turbines

. The development of electricity as a source of energy available to everyone leads to the use of windmills as an additional possibility for generating electricity. Basic developments in the field of aerodynamics. The period ended due to cheaper fossil oil.

1930–1960: First phase of innovation

. The necessity of electrifying rural areas and the shortage of energy during the Second World War stimulated new developments. Advances in the field of aerodynamics. The period ended because of cheaper gas and fossil oil.

From 1973: Second innovation phase and mass production

. The energy crisis and environmental problems in combination with technological advances ensure a commercial breakthrough.

Figure 1.1 Historical development of the use of wind as a source of energy. The first and last periods have had the greatest effects on society

During the classical period, the ‘wind devices’ (windmills) converted the kinetic energy of the wind into mechanical energy. After direct current and alternating current generators were invented and came to be used for public power supply, windmills were used for electrical power generation. This development began effectively in the late nineteenth century and, after the energy crisis in 1973, became a great economic success.

In order to differentiate clearly between the different plants, they are called windmills or wind turbines in this book.

1.2 The First Windmills: 600–1890

Water mills were very probably the precursors of windmills. Water mills, again, were developed from devices that were operated by people or animals. The devices that are known to us from historical sources possessed a vertical main shaft to which cross bars were attached in order to drive the main shaft. The cross bars were operated by farm animals such as horses, donkeys or cows. It seems only logical that the vertical windmills developed from these devices. However, there are few historical sources to provide proof of this. More sources can be found on the ‘Nordic’ or ‘Greek’ water mills that evolved from the animal-operated devices (see Figure 1.2). These types of water mills had their origin about 1000 BC in the hills of the Eastern Mediterranean area, and were also used in Sweden and Norway [1].

Figure 1.2 Water wheel with vertical axis of rotation near Göteborg, Sweden. From Ernst, The Mills of Tjorn (1965) published by Mardiska Museet, Stockholm [2]. Reproduced with permission of Mardiska Museet, Stockholm

The first windmills with vertical main shafts were found in Persia and China (See Figures 1.4). In the middle of the seventh century AD, the building of windmills was a highly prized trade in Persia [3]. In China, vertical windmills were introduced by traders. The first European to report on the windmills in China was Jan Nieuhoff, who travelled there in 1656 with one of the Netherlands ambassadors. Figure 1.3 shows an illustration by Jan Nieuhoff [4]. Similar windmills were in use in China until quite recently (see Figure 1.4).

Figure 1.3 Drawing of Chinese windmills in Paoying (Chiangsu) by Jan Nieuhoff, 1656 [4]. Reproduced with permission of Cambridge University Press

Figure 1.4 Left: Chinese wind wheels at Taku that pump brine solutions for the extraction of salt (Hopei [3]). Reproduced with permission of E & F N Spons; right: schematic depiction of the function of a Chinese windmill. Solid lines represent blades and dash-dotted lines represent sails [5].

Other types of devices were treadmills that were operated by the bodily strength of people or animals. Spades were arranged radially to the main shaft. The horizontal water mill developed from the treadmill by the replacement of people or animals by flowing water. A further development in the first century AD was the so-called Vitruvian water mills, which were introduced by the Roman Vitruvius. This water mill can be seen as the prototype for the undershot water mill that can be found throughout Europe in rivers and streams with low water-level differences. Also, it is assumed that the Vitruvian wheel is the forerunner of the horizontal windmill [1].

The first horizontal windmills were found during the crusades in the Near East and later in northwest Europe. These windmills possessed a fixed rotor construction that could not be rotated in the wind (yawing). The rotor blades of these windmills were similar to those that can be seen today, for instance, on the Greek Island of Rhodes. By about 1100 AD there were reports of fixed post mills that were positioned on the city walls of Paris. It is unclear whether the windmills that were widely distributed came from the Near East to Europe or were reinvented in Western Europe. Some authors even doubt the existence of horizontal windmills in the Near East during the Crusades [3,6]. Others, again, speak only of vertical windmills at that time [4,7].

Figure 1.5 A vertical axle windmill from the year 1718 [2]. Reproduced with permission of Hugh Evelyn

The assumption that the windmills of Western Europe were invented independently of those of the Near East is supported by documents that have been found in the archives of the Netherlands Province of Drenthe. In these documents that originate from the year 1040, at the time of the Crusades, there is mention of two windmills (Deurzer Diep and Uffelte). During the Renaissance some vertical windmills were also built in Europe (see Figure 1.5). Especially well known was the windmill built by Captain Hooper in Margate, England [2].

1.2.1 Technical Development of the First Horizontal Windmills

The first windmills possessed no yaw mechanisms and the blades consisted of a frame of longitudinal and lateral bars through which sailcloth was tied (see Figure 1.6, left). The power output was controlled in that the sail was wholly or partly furled up by hand (see Figure 1.6, right).

Figure 1.6 Left: a post windmill of the early fourteenth century (British Museum) [2]. Reproduced with permission of Hugh Evelyn; right: ‘power control’ of a classical windmill [8]

For reasons of statics, the main shaft had an angle of inclination (dimension of the milling building, the axle load on the axial sliding bearing, the possibility of erecting a load-bearing building or a conical tower for stabilisation).

The development of the classical windmill in Western Europe will be described before investigating the global development of windmills into wind turbines with which electrical power is generated today.

Although the wind comes mainly from a particular direction in the windy regions of Europe, the wind direction varies so strongly that a yaw mechanism makes sense in order not to lose too much energy with side flows of the wind. This requirement led to the first post windmills (see Figure 1.7), which could be yawed into the wind. These windmills were used for milling corn. By means of a strong beam attached to the mill building, the whole house, which stood on a fixed substructure, could be turned until the rotor was vertical to the wind.

Often the support beams of the substructure were covered with wooden planking so that a storeroom was created. The millstone and the gear wheels were situated in the rotating mill building. One of the first depictions of this type of windmill, dating from the year 1299, comes from a convent in Oedenrode, in the Noord Brabant region in the Netherlands.

Another attempt to turn the rotor into the wind was attempted by building a windmill on a floating platform. The platform was fixed by means of a joint to a pile that was sunk into the ground of a lake in the north of Amsterdam in 1594. Probably because of the lack of stability, such a windmill was never built again, but the concept can be taken as the first attempted offshore wind turbine.

Figure 1.7